EM6517 ETC, EM6517 Datasheet - Page 29

• Manufacturer Part Number: EM6517
• Description: 4 BIT MICROCONTROLLER
• Manufacturer: ETC

9
The EM6517-1 has simple Serial Write Buffer which outputs serial data and serial clock.
Serial Write Buffer clock frequency is selected by bits SWBFSel0 and SWBFSel1 in RegSWBCntl register. The
possible values are 1kHz (default), 2kHz, 8kHz or 16kHz.
The signal TestVar[3], which is used by the processor to make conditional jumps, indicates "Transmission
finished" in automatic send mode or "SWBbuffer empty" in interactive send mode. In interactive mode,
TestVar[3] is equivalent to the interrupt request flags stored in RegIRQ[i] registers : it permits to recognize the
interrupt source. (See also the interrupt handling section 13 for further information). To serve the "SWBbuffer
empty " interrupt request, one only has to make a conditional jump on TestVar[3].
The SWB data is output on the rising edge of the clock. Consequently, on the receiver side the serial data can
be evaluated on falling edge of the serial clock edge.
Normally the Clock and the Data output terminals are always driven to ‘0’ outside a SWB data transfer. With a
metal option one can put the Data output, the Clock output or both into a high impedance state outside of a SWB
transfer. Refer to 19.1.4 for the mask settings. The timing going into high impedance state into SWB transfer
and back into high impedance is depending on the selected mode, interactive or automatic.
Figure 22. Serial Write Buffer Architecture
SWB has two operational modes, automatic mode and interactive mode.
9.1 SWB Automatic send mode
Automatic mode enables a buffer on a predefined length to be sent at high transmission speeds up to ck[15]
(16kHz). In this mode user prepares all the data to be sent (minimum 8 bits, maximum 256 bits) in the RAM.
The user then selects the clock speed, sets the number of data nibbles to be sent, selects automatic
transmission mode (SWBAuto bit set to 1) and enters STANDBY mode by executing a HALT instruction. Once
the HALT instruction is activated the SWB peripheral module sends the data in register RegSWBuff followed by
the data in the RAM starting at address 00 up to the address specified by the bits size[5:0] located in the
RegSWBSizeL, RegSWBSizeH registers.
DB[3:0]
Serial (Output) Write Buffer - SWB
Addr. Counter
SW BFSel0,1
Size[5:0]
RAM
FOR ENGINEERING ONLY
SW Bauto
Control
Logic
Clk
Mux
SW BStart
SW B buffer
Shift register
TestVar3
© EM Microelectronic-Marin SA, 09/99, Rev. A/277
SW B buffer
IRQ (only in
interactive
register
SW B data
EM6517
SW B clock
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